There has been a long-standing debate among condensed-matter physicists about the origin of the pseudo-gap state in high-temperature superconducting cuprates. Polarized neutron diffraction has revealed the existence of an ordered magnetic phase, hidden inside the pseudo-gap state of underdoped YBa2Cu3O6+x, HgBa2CuO4+d and Bi2Sr2CaCu2O8+d [1]. Interestingly, the ordering temperature matches the pseudo-gap temperature T* deduced from resistivity measurements. The magnetic order can be described as an Intra-Unit-cell magnetic order, breaking timereversal and C4 rotational symmetries. It corresponds to the symmetry predicted in the loop current theory of the pseudo-gap state where staggered current loops give rise to orbital-like magnetic moments within the CuO2 unit cell. We will review these observations in light of the loop current model. Other proposals, based on magneto-electric quadrupoles, will be presented as well. Recently, we observed similar magnetic signal in the antiferromagnetic iridates system Sr2(Ir,Rh)O4 [2] below a temperature different from TN suggesting the existence of loop-current electronic states in different oxides.

“collaborators: Lucile Mangin-Thro, Jaehong Jeong, Yvan Sidis (LLB-Orphée), Yuan Li (Peking University), Yang Tang, Martin Greven (Minnesota University),Véronique Brouet (LPS Orsay) .

Email: philippe.bourges@cea.fr
[1] P. Bourges and Y. Sidis, C. R. Physique, 12, 461, (2011); Y. Sidis and P. Bourges, J. Phys.: Conf. Ser. 449, 012012 (2013). L. Mangin-Thro et al., Phys. Rev. B 89, 094523 (2014). L. Mangin-Thro et al., Nat. Comms. 6, 7705 (2015) & Phys. Rev. Lett., 118, 097003, (2017). [2] Jaehong Jeong et al, Nat. Comms., 9, 15119 (2017).
[2] Jaehong Jeong et al, Nat. Comms., 9, 15119 (2017).